The removal of carbonyl sulfide from liquified hydrocarbon gases consisting principally of C.sub.3 hydrocarbons, C.sub.4 hydrocarbons and their mixtures is troublesome and costly. Usually, the stream will also contain hydrogen sulfide, which is readily removable from the gas stream. If, however, the carbonyl sulfide is allowed to remain in the liquified petroleum hydrocarbon and if water is present, it will, with time, undergo the hydrolysis reaction: EQU COS+H.sub.2 O.fwdarw.H.sub.2 S+CO.sub.2
to yield hydrogen sulfide which will make the liquified hydrocarbon gas off specification.
While the reaction is reversible, the reaction equilibrium constant is so high that if equilibrium is achieved, the COS becomes insignificant and the H.sub.2 S becomes the significant sulfur species.
In U.S. Pat. No. 2,594,311 to Johnson et al, there is described the use of a solution of caustic soda containing a small percentage of monoethanolamine to effect removal of COS at elevated temperatures. The carbonyl sulfide reacts irreversibly with the reagent, causing it to become spent. The products of the reaction must be discarded and replaced, either continuously or in batch quantities. This is costly, both with respect to the cost of replenishing the caustic and the loss of monoethanolamine, which cannot be recovered readily from the spent caustic. In addition to the chemical cost, disposal of the spent materials poses a problem from a pollution standpoint.
It would be desirable, therefore, to provide a process for the purification of liquified hydrocarbon gases, also known in the trade as liquified petroleum gases or LPG, which does not involve high chemical costs or create a problem of pollution to the environment.